Art of making closure seals by molding and curing



C. E. MAIER Oct. 13, 1953 ART OF MAKING CLOSURE SEALS BY MOLDING ANDCURING Filed July 27, 1950 mma .WMU Wma Ww QM.

lb .H

w MS* VW, @dal @lah r/d/paww,

Patented Oct. 13, 1953 ART F MAKING CLOSURE SEALS BY MOLDING AND CURINGCurtis E. Maier, Riverside, lll., assignor to Continental Can Company,Inc., New York, N. Y., a corporation of New York Application July Z7,1950, Serial No. 176,217

(Cl. lll-59) Claims. l

This invention relates to the rapid production of crown closures forcontainers, including the forming of a shaped cushion pad or sealingmember.

It has been proposed and is a practice to form such crown seals with theusual metal shell having a cushion pad therein, made of rubbercomposition, or of a like elastomer compound. However, when thecomposition was introduced in the form of a solution or emulsion, forthe necessary liquidity of application, rotation of the shell isrequired for distribution, the composition is not form-maintaining initself, a lengthy period is required for elimination of the solvent orlike vehicle, and the distribution cannot be controlled with assuredaccuracy, nor can special contours in the sealing area or in the centerbe attained for maximum sealing efliciency and minimum use of material.Also, curing could only be effected after such solvent was eliminated.On the other hand, when the composition was introduced as a blank, carewas required for producing the necessary adhesion in the crown shell andhigh pressures and temperatures were required for molding. Further, ifthe blank or disc is out out from a web, either frame scrap loss orreworking cost is involved; and at least one additional operation isinvolved in cutting and placing the blank or disc.

When a crown seal is to be used for capping a bottle or other container,the cushion pad serves to conform to the possibly irregular lip of thecontainer, providing a gasket between such lip and the closing face ofthe metal crown shell itself. The crown seal usually has a furtherdemand upon it, being that of preventing contacts of the contents of thecontainer with the metal at the inner face of the crown shell. These tworequirements may be satised by materials insoluble and essentiallynon-permeable to the contents of the container, but in practice suchmaterials do notdemand as great a thickness for protection againstpenetration as is required for providing the necessary sealing gasketfor conformation to the container lin. Accordingly, it is preferred inaccordance with this invention to provide a crown seal in which thesealing member or cushion pad has a thick outer annular portion forengagement with the container lip, and a thinner central portion toprovide the assurance against contact of the contents of the containerwith the metal of the crown shell.

It has been found that by using compositions formed by dispersing iineparticles of resinin a liquid plasticizer, a composition is obtainedwhich can be used in liquid condition and a measured I amount placed ina crown shell :and then shaped and cured by heating the crown shell anda shaping punch for producing a. temperature in the plasticizer whichcauses it to dissolve the resin, so to speak, so that a substantiallyuniform, thermoplastic, shaped cushion pad is produced: and thereafterto cool the same so that the established shape is thereafter maintainedunder the conditions of service. That is, the resin fuses or dissolvesinto the said plasticizer to establish such amass.

By such practice, there is no :material loss, as the measured amount ofliquid is delivered into each shell; there is no volatile component tobe driven oit; the composition can be molded under low pressures, sothat the equipment need not be designed for high pressures; the compoundcan be molded easily to produce a iinal article having the optimumcontour for economy in material and performance as a seal; and atappropriate and easily attainable temperatures the pasty compound isfused or iiuxed to form a tough resilient liner within a time which isvery short compared to that for curing rubber or like compositions orfor driving water or solvents out of liquid compositions containing thesame as a distributing or fiuidifying agent. w

An example of practice of the invention is shown on the accompanyingdrawing, in which- Flg. l is a diagrammatic showing of the successivesteps of producing a crown seal according to this invention and Fig. 2is an axial cross-section through such a crown seal.

In Fig. l, a series of crown shells I0 are shown advancing through theseveral steps of operation.

The crown shells may be prepared in the customary fashion by providing asheet of steel or tin plate, with lithographed advertising matter on oneface, and with a coating of a lacquer at the other or inner face, asmore closely described hereinafter. The sheets thus coated and baked arethen passed through punch presses in the presently customary fashion,for example, whereby several hundred such crown shells are blanked andformed from a single sheet.

The composition of resin particles with plasticlzer, the resin beingessentially insoluble in the terial as a iluidifying agent, which mustbe expelled to produce the nal gel: and since the action is largely oneof iluxing or inter-solution of the resin and plasticizer, there isessentially no change in volume as the hot mixture changes to the gelform.

Such aV crown shell may then be started through the present procedure,as indicated by Fig. 1. 'I'he rst step after introduction to theprocedure is that of introducing into the concaveupward crown shell aquantity of the mixture of vinyl resin and plasticizer. The presentpreference is for the crown shell to be cold when the deposit begins;but it maybe preheated if desired. This deposit may be accomplished bywarming the material to a temperature of about 110 to 115 F., tofacilitate ow, and then pass it to and through the nozzle II and providea deposit of a standard quantity in theV crown shell I2 as shown beneaththe said nozzle. The

nozzle and material may be kept warm by infrared radiation from theindicated electric bulb I3. It has been found that a volume of 100 to400 cubic millimeters is a desirable quantity, the smaller volumes beingusable with short-skirt shells, and the larger volumes with theso-called standard-skirt shells; it being understood that smallervolumes are permissible when the containers to be sealed are knowntohave close tolerances for irregular lip surfaces as compared with somebottles where greater allowances by greater thicknesses of cushions andcorresponding larger volumes of paste are required. In general, thelower limit of volume for a specific employment depends upon the degreeof sealing efficiency required'as the sealing eiiiciency decreases withthe volume of compound, particularly in the lower ranges. The upperlimit depends upon the amount of compound that can be put into the shellwithout'interfering with the sealing, and on economies. Under theseconditions, the introduced material I4 forms a button of aboutthree-eighths of an inch to three-quarters of an inch diameter at thecenter of the cap, as indicated by the mass I6 in the crown shell I 1,which indicates a crown shell between the time of delivery of thecomposition into the same, and the time of molding and curing thecomposition.

The crown shell, with the button of composition therein, is then broughtto a heating platen illustrated as a hot plate having a heater 2ltherebeneath, and providing an upper surface upon which rests a crownshell 22 having therein a charge of composition which is undergoingmolding and curing. For the purpose of shaping the mass, a punch'23,having an outer diameter closely corresponding to the inside diameter ofthe crown shell, is moved down into the crown shell. This punch isillustrated as having heating means such as the electric heating wire 24therein. The lower'end of the punch can have a shaped projection 25, oflesser diameter and extending below the general annular area, at thecenter of the bottom of the punch.

Under the influence of the heat delivered into the mass from the hotplate 20 and the heated punch 23, the composition flows under thepressure, and establishes a shape determined by the crown shell actingas a mold, and by the punch acting to form the later-exposed surface ofthe cushion piece. The temperature and pressure are maintained untilthis fluidizing has caused the material to assume the intended finalform, and until the resin particles have fused into the plasticizer, andthe entire mass has become homo- 4 geneous and form-maintaining at thetemperature of treatment.

The article thus produced, as shown in Fig. 2, has the usual circularmetal closure portion 30, and the crimped skirt wall 3 I. The outersurface of these metal parts has the coating 32, which may includeadvertising matter over the area 30, for example, together with aninternal lacquer coating 32 on the skirt walls 3|. The cushion pad ofthe shaped and cured mass is formed by a thin central portion 33, and athicker annular portion 34: this cushion pad or sealing member as awhole having its surface adjacent the part 30 of the crown shell adheredto the internal lacquer coating 32' originally provided on the metalsheet, so that a secure and tight bond exists therebetween. 'Ihe lacquerfor the inner surface of such compound lined crowns may desirably beselected in accordance with the material employed for the compound andin accordance with the intended contents of the container to be sealed.For example, a vinyl lacquer prepared as described in the Maier et al.Patent 2,380,456, with per cent of vinyl chloride-vinyl acetatecopolymer resin and 20 per cent of oleoresinous modifier produces asatisfactory adhesion. When the crown seals are to be employed withcarbonated beverages, itis preferred to employ a trimer lacquer having acorresponding solids formulation of 80 per cent of vinyl chloride-vinylacetate copolymerized in the presence of maleic anhydride as a modifier,for example, in the respective ratios of 87:12:1, together with 20 percent of a phenolic resin derived from ortho-cresol and formaldehyde.Either of these lacquers can be prepared in an organic solvent, such as70% Xylol and 30% isophorone, with 20% solids, for roller coating, Forspraying, more volatile solvents, such as toluol, methyl ethyl ketone,and methyl isobutyl ketone, can be used. After applying and drying, thecoating is baked.

The composition forming the principal mass of the shaped cushion pad hastwo basic ingredients comprising an elastomer and a plasticizertherefor, the plasticizer being so selected that the elastomer isessentially insoluble therein at room temperature, but is soluble atsome elevated temperature. These two ingredients are ground together toform a paste which is flowable under the conditions stated, and may alsoinclude other components such as inert fillers to limit cutting,pigments, modifying resins to assist control of physical properties,stabilizers for the resins and other components, waxes to preventblocking and to reduce moisture vapor and gas permeability, etc.However, vthese other materials are not essential in the composition,but may be employed to contribute to the desired properties for theparticular employment. In general, the formulations described in theFoye United States Patent 2,489,407 or in South African Patent 2,556/47may be employed, noting that the filler anddother components may beomitted if so 'desire The elastomer component may be a vinyl resin ofthe class inclusive of polyvinyl chloride, copolymers of vinyl chlorideand vinyl acetate such as the 97:3 per cent copolymer, vinylidenechloride polymers, and copolymers of vinyl chloride and vinylidenechloride. The chloride content should be high, when the seal is toresist aqueous liquids; such as 90 per cent vinyl chloride in acopolymer.

Among the plasticizers useful are those which have a very slow wettingor dissolving action upon the selected vinyl resin at room temperatureand at temperatures up to around 115 F. The ester type plasticizers ofvinyl resins have this general characteristic, and require highertemperatures for producing penetration, diffusion, and intersolution. Apreferred plasticizer is dioctyl phthalate; others are dibutylphthalate, dioctyl sebacate, and tricresyl phosphate. The plasticizershould be liquid at the temperature of use.

The ratio of the elastomer and plasticzer, by weight, may be from 6:4 to4:6, with preference for a ratio of about 1:1.

Such compositions can be introduced at about 110 to 115 F. through thenozzle Il, and then caused to flow, be shaped, and cured, by the actionof the hot plate 20 and the heated punch 23, resulting in the productionof a resilient, tough plasticized resin mass.

Illustrative of the condition for the molding and curing operation isthe employment of 10 to 30 pounds pressure per square inch in a crownshell having a one-sixteenth inch radius at the top corner, or 10 to 100pounds per square inch in a crown shell having a three thirty-secondsinch radius at the top corner, with the punch designed as shown in Fig.l, to produce a smooth frusto-conical surface for the annulus 34 shownin Fig. 2. In general, the pressure is dependent (a) upon the design ofthe punch, the more complex shapes of seals requiring higher moldingpressures; and (b) upon the volume of compound being used, as higherpressures are desirable with the lower volumes.

The temperature employed for causing the fiow and molding of thecomposition to shape, in

practice, depends upon the characteristics of the original coatinglacquer 32. When this lacquer is of vinyl chloride-acetate polymer, withthe oleoresinous modifier as described above, the temperature can rangefrom 275 F. to 350 F.: when the so-called trimer of vinylchloride-acetate and maleic anhydride with O-cresol phenolic resin isemployed, the temperature may range from 300 F. to 375 F.

The time required for heating and molding is only two or three seconds:the additional time required for completing the diffusion and curing inthe mold depends upon the temperature and pressure conditions used. Forexample, using a temperature of 325 F. and 30 pounds per square inchpressure, the time required for producing a completed cure with a 97:3vinyl chloride-acetate copolymer, with dioctyl phthalate plasticzer, isfrom four to thirty seconds: a stable and formmaintaining body resultsin two to three seconds, and a thorough diffusion and generalhomogeneity occurs within thirty seconds. In general, it is preferred toemploy relative higher temperatures, to shorten the total time. However,the materials are of low heat-transmission, so that about six seconds ispresently regarded as a commercially minimum time under a condition suchas 375 F. with 75 pounds per square inch pressure.

As a specific example, with the use of the trimer lacquer upon theinterior of the crown shell, a temperature of 350 F., and a pressure of25 pounds per square inch, six seconds was found to produce asatisfactory molding and curing cperation, for producing a liner havinga frusto conical annular surface in a crown shell having a one-sixteenthinch radius at the top corner. When the crown shell had a threethirty-seconds inch radius at the top corner, the pressure was increasedto 30 pounds per square inch, for producing a molding and curing in sixseconds at a temperature of 350 F.

While the invention has been illustrated by a practice of making crownseals with lacquered metal shells, and employing the stated materialsand conditions, it will be understood that it may be embodied in otherforms within the scope of the appended claims.

I claim:

l. The method of forming sealing pads for closure seals, which comprisesdepositing in a closure shell having an internal. lacquer coating, ameasured quantity of a semi-liquid paste composition consisting foressential components thereof of a normally liquid plasticizer and afinely divided resin which is paste-forming with the plasticizer at atemperature below the fluxing temperature of the resin-plasticzercomponents, said composition being substantially free from vaporizablecomponents and'capable, upon being heated to the fluxing temperature ofthe resin-plasticizer components thereof and thereafter'being cooled, offorming al permanent rubbery gel having essentially the same volume assaid measured quantity, pressing a heated forming plunger into sealingrelation with the shell and against the deposited material for shapingthe same into a sealing pad of the desired contour, and maintaining saidshaped pad under heat and pressure at a fluxing temperature until theshaped pad has adhered to the closure shell and the saidresin-plasticzer components have fiuxed togather.

2. The method of making crown seals having therein a shaped and curedcushion pad, which comprises providing a crown shell having an internallacquer coating exhibiting a vinyl resin at the exposed side thereof,depositing in the crown shell and upon said exposed coating face thereofa measured quantity of a semi-liquid mass essentially free fromvaporizable components comprising particles of a vinyl resin dispersedin a fluid vinyl resin plasticzer, heating the mass and concurrentlytherewith confining and compressing the saine in the crown shell by aheated shaping surface while heating and thereby shaping the mass andprovoking adhesion of the mass to said lacquer coating and dissolutionof the vinyl resin particles into the plasticizer to constitute anessentially uniform mass of the same volume as said measured quantity.

3. The method of forming sealing pads for crown seals, which comprisesdepositing at a temperature of about 110 to 115 F. into a lacqueredmetal crown shell a.` measured quantity of to 400 cubic millimeters of asemi-liquid paste composition substantially free from vaporizable`components and consisting essentially of a finely divided vinyl resinand a normally liquid ester plasticizer of the vinyl resin which forms afluid paste with the resin at said temperature, said composition beingcapable upon being heated to a fiuxing temperature of 275 to 375 F. andthereafter being cooled, of forming a permanent rubbery gel of the samevolume as said measured quantity, pressing a heated forming plungeragainst the deposited material for confining and shaping the same into asealing pad of the desired contour, and maintaining said shaped pad at275 to 375 F. and under a pressure of 10 to 100 pounds per square inchuntil the shaped pad has adhered to the closure shell and the saidresin-plasticizer components have fiuxed together.

4. The method of making crown seals having therein a shaped and curedcushion pad, which comprises providing a crown shell having an internallacquer coating, depositing in the crown shell and upon a part of saidcoating a measured quantity of a semi-liquid pasty mass essentially freefrom vaporizable components comprising particles of a resin disposed ina fluid plasticizer of the resin, heating the mass, and pressing aheated forming surface upon the mass in theA crown shell while soheating and thereby distributing and shaping the mass and provokingadhesion of the mass to said lacquer coating, and fluxng of the resinparticles with the plasticizer to constitute an essentially uniformmass.

5. The method of making closure seals, which comprises depositing at atemperature of fluid .flow into a cold internally-lacquered closureshell a measured quantity of resin paste essentially free fromvaporizable components having as dominant gel-forming elements thereofnely divided resin particles suspended in a resin plasticizer Which isnot an active solvent of the resin at said temperature of fluid flow ofthe resin paste and which is an active solvent thereof at a higher anduxing temperature, pressing a forming surface against the deposit andthereby distributing and shaping the same, and then heating the shelland surface and maintaining the deposit at a fluxing temperature andconfined between the shell and said surface until the resin andplasticizer have fluxed together and constitute a form-maintaining geladherent to said shell and having the same volume as said measuredquantity.

CURTIS E. MAIER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,486,937 Taliaferro Mar. 18, 1924 2,489,407 Foye Nov. 29,1949 2,498,489 Haggart Feb. 21, 1950 FOREIGN PATENTS Number Country Date500,298 Great Britain Feb. '7, 1939

